The invention relates to an in-focus detector for a binocular stereoscope, and more particularly, to an in-focus detector which is used in a binocular stereoscope to derive a control signal to automatically bring the microscope into focus.
As is well recognized, binocular stereoscopes are extensively used in various fields including medical operations, examinations, the machining of miniature parts and the like. An object being examined is frequently subject to a rapid movement, and in such instance, it is necessary that the focusing operation must be repeated each time the object has moved. In particular, when the both hands of an observer are occupied with other operations, such frequent focusing operation is very troublesome to perform. In addition, binocular stereoscopes are often of a low magnification and an increased depth of focus, which result in a poor accuracy being achieved by a manual focusing operation because of the inherent focusing effects of the eyes. Hence, if a photograph is taken under such condition, it is highly likely that an out-of-focus photograph may be obtained.
In view of the foregoing, it will be appreciated that there has been a strong need for a binocular stereoscope having an automatic focusing function which enables the stereoscope to be automatically maintained in focus upon an object being examined.
In considering an optimum in-focus detection technique which is applicable to an automatic focusing function of an binocular stereoscope, it will be seen that an in-focus detection technique of double image coincidence or vertical image alignment type will minimize the requirements for added optics to the microscope and facilitate its incorporation into the microscope inasmuch as the microscope is originally provided with a pair of left- and right-hand observation optics. An in-focus detection technique of the contrast type may also be contemplated in which an in-focus condition is detected by evaluating the sharpness of an image of an object being examined which is produced by one of the observation optics. However, as mentioned previously, the increased depth of focus of a binocular stereoscope may result in reduced accuracy. As compared with this technique, an in-focus detection technique of double image coincidence or vertical image alignment type detects an in-focus condition by determining any displacement in the position of a pair of images formed for a single object being examined, and thus permits a high accuracy to be achieved. As a result, this focusing technique is best in a binocular stereoscope.